Personal audio devices, including wireless telephones, such as mobile/cellular telephones, cordless telephones, mp3 players, and other consumer audio devices, are in widespread use. Such personal audio devices may include circuitry for driving a pair of headphones or one or more speakers. Such circuitry often includes a speaker driver including a power amplifier for driving an audio output signal to headphones or speakers.
In many audio output systems, it is desirable to have low latency, wherein latency may be defined as a duration of time it takes a digital audio input signal to be processed and reproduced as audible sound by a transducer. An example of a scenario in which low latency is desired is noise cancellation using one or more microphones in a feedback or feed forward system. It is often desirable for such audio system to operate at a high dynamic range with low power. Many will be battery operated and operate under a wide range of audio levels.
Out-of-band noise (e.g., noise at ultrasonic frequencies) present within an audio signal may cause undesirable dissipation of power in drivers, amplifiers, and other components of an audio system. Out-of-band noise may also spectrally fold into the audible audio band, leading to undesirable noise. Accordingly, to maximize dynamic range and minimize power, it may be desirable to reduce or eliminate out-of-band noise from an audio signal using out-of-band filtering. However, out-of-band filtering may introduce undesirable delay into an audio path.